A PDF looks like a finished, flat page. Underneath, it is a structured file with room for plenty of information about its author, its history and the software that made it. Before you send a contract, a CV or a report, it is worth knowing what is in there.
The Info dictionary
Every PDF may include a small table of document properties:
| Key | What it usually holds |
|---|---|
| Title | The document title, or often the original file name, e.g. "Draft v7 – confidential" |
| Author | Taken from the user account of the person or software that created it |
| Subject, Keywords | Free text. Sometimes internal project names. |
| Creator | The application, such as a word processor or design tool and its version |
| Producer | The PDF library or "Save as PDF" engine that wrote the file |
| CreationDate, ModDate | When it was made and last changed, with timezone |
XMP metadata
Many files also include an XMP packet: an XML document that repeats and extends the Info dictionary, with fields like document and instance IDs, history of edits, template names and the tool chain. Removing the Info dictionary alone leaves this behind, so a proper cleaner removes both.
Things that are not "metadata" but still identify you
- Comments and annotations store the author name of every sticky note and highlight.
- Form fields may contain values that were typed and later hidden.
- Attachments are embedded files that remain inside the PDF.
- Incremental saves. Some editors append changes rather than rewriting the file, so older versions of a page, and text that has since been "deleted", stay inside.
- Hidden layers, bookmarks and alt text can repeat content that is not visible on the page.
- Digital signatures name the signer and the certificate.
A quick way to look
Most PDF viewers show some of this under File → Properties or Document Properties. That only shows the Info dictionary. For a full picture drop the file into the Metadata Remover: it lists the Info fields and any XMP, then removes them and shows you that they are gone.
Practical habits
- Before sending a PDF to the outside world, clean its properties.
- Use "Save as" or "Export" to a fresh PDF rather than sending a heavily edited file with a long history.
- Check comments, attachments and form fields too.
- If content itself is sensitive, remove it with true redaction, not with a cover-up.
- Keep your original, since cleaning produces a new file.
Does cleaning affect the content?
No. Pages, text, fonts and images are unchanged. Only the descriptive data is removed. Note that cleaning invalidates digital signatures, because the file has changed.
Try it yourself
Use the Image & PDF Metadata Remover. It runs in your browser and your files stay on your device.